1. Field of the Invention
The present invention relates to projection display apparatuses that with illumination light illuminate images formed on light valves and that by means of projection lenses enlarge and project the images on a screen, and relates to light source devices used in such projection display apparatuses.
2. Description of the Background Art
Discharge lamps are widely employed as light sources for projection display apparatuses using liquid-crystal or minor-deflection type digital micromirror devices (DMDs) for light valves. Discharge lamps, however, carry with them problems of short lifespan and poor reliability.
In order to solve these problems, projection display apparatuses that use, as the light sources, solid-state light sources such as semiconductor lasers or light emitting diodes (LEDs) have been suggested.
However, with projection display apparatuses using trichromatic red, green and blue laser light sources, there are image quality problems in that speckles stand out, especially in green light. Further, with light sources using trichromatic red, green and blue LEDs the light emitting efficiency, especially of the green LEDs, is poor, such that improving projection display apparatus brightness has been an issue.
Therefore, as a separate technique for enhancing brightness in projection display apparatuses using solid-state light sources, a light source device in which a number of different types of solid-state light sources are combined with a fluorescent material that fluoresces on being excited by light from the solid-state light sources has been suggested.
In implementations utilizing a configuration in which blue light is obtained from a laser light source, red light is obtained from an LED, and green light is obtained by exciting a fluorescent material by utilizing the laser light source used for the blue light, insufficiency in the amount of green light can be overcome. Green light insufficiency is a problem with illumination devices using green LED light sources or green laser light sources, which are poor in light-emitting efficiency. The structure just described may therefore be advantageous.
On the other hand, in the configuration in which a blue laser light source and a green fluorescent material are combined with each other, an LED is used as a red light source. Therefore, if brightness of the illumination device is to be further enhanced, improving the red light output becomes an issue. However, while the output power of a blue laser light source and of green fluorescence from excitation using the blue laser light source are relatively easily enhanced, output power of a red LED light source is significantly difficult to improve with there being just a single one.
Further, in order to represent video images in a natural manner it is necessary that the light source employed in the illumination device include light of the three primary colors, red, blue and green. Therefore, if the output power is increased in a configuration in which blue light is obtained from a laser light source, red light is obtained from an LED, and green light is obtained by exciting a fluorescent material with blue light using the laser-light source employed, the red light will be insufficient. Consequent problems have been that the balance among red, blue and green necessary for representing white is upset, spoiling the impression of white, or otherwise that when a video image is represented, it turns out to be an image in which the red alone is dark.
Therefore, in order to enhance brightness while preserving a balance in the intensities of the red, blue and green light, each of light sources for red, for blue, and for green light presumably could be constituted from a plurality of identical light sources.
However, in conventional projection display apparatuses employing fluorescent materials, light sources of a plurality of colors being independently present means the number of parts is large. Therefore, if a conventional projection display apparatus is simply configured with a plurality of light sources for each color in order to enhance the brightness, the number of parts would be further increased.